Datasheet

Thermal Protection
Power Dissipation
P
D
+
ǒ
V
IN
* V
OUT
Ǔ
I
OUT
(6)
Package Mounting
TPS73719-Q1
TPS73733-Q1
SBVS123 – DECEMBER 2008 ........................................................................................................................................................................................... www.ti.com
Thermal protection disables the output when the junction temperature rises to approximately 160 ° C, allowing the
device to cool. When the junction temperature cools to approximately 140 ° C, the output circuitry is again
enabled. Depending on power dissipation, thermal resistance, and ambient temperature, the thermal protection
circuit may cycle on and off. This cycling limits the dissipation of the regulator, protecting it from damage due to
overheating.
Any tendency to activate the thermal protection circuit indicates excessive power dissipation or an inadequate
heatsink. For reliable operation, junction temperature should be limited to 125 ° C maximum. To estimate the
margin of safety in a complete design (including heatsink), increase the ambient temperature until the thermal
protection is triggered; use worst-case loads and signal conditions. For good reliability, thermal protection should
trigger at least 35 ° C above the maximum expected ambient condition of your application. This produces a
worst-case junction temperature of 125 ° C at the highest expected ambient temperature and worst-case load.
The internal protection circuitry of the TPS737xx has been designed to protect against overload conditions. It
was not intended to replace proper heatsinking. Continuously running the TPS737xx into thermal shutdown
degrades device reliability.
The ability to remove heat from the die is different for each package type, presenting different considerations in
the PCB layout. The PCB area around the device that is free of other components moves the heat from the
device to the ambient air. Performance data for JEDEC low- and high-K boards are shown in the Power
Dissipation Ratings table. Using heavier copper will increase the effectiveness in removing heat from the device.
The addition of plated through-holes to heat-dissipating layers also improves the heatsink effectiveness.
Power dissipation depends on input voltage and load conditions. Power dissipation (P
D
) is equal to the product of
the output current times the voltage drop across the output pass element (V
IN
to V
OUT
):
Power dissipation can be minimized by using the lowest possible input voltage necessary to assure the required
output voltage.
Solder pad footprint recommendations for the TPS737xx are presented in Application Bulletin Solder Pad
Recommendations for Surface-Mount Devices (SBFA015 ), available from the Texas Instruments web site at
www.ti.com .
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